1. Field of the Invention
The present invention relates to an electrical circuit for testing the electrical integrity of an inductive coil, solenoid, or the like. More particularly, the present invention is concerned with a circuit including a computer for testing whether the coil, solenoid, or the like has an open circuit or a short circuit.
2. Description of the Prior Art
Many machines and articles of manufacture use inductive coils, solenoids, or the like to perform various important functions. For example, a magnetic coil might be used to count revolutions of a rotating member whereby a metal segment on the rotating member induces a voltage pulse in the magnetic coil with each revolution of the member. Additionally, for example, solenoids are used to actuate hydraulic cylinders.
In many of these applications a failure of the coil or solenoid may be undetected and may lead to serious consequences if the coil or solenoid failure remains unknown. For example, if a magnetic sensor coil becomes short circuited or electrically open, it will not respond to the passage of the metal segment to induce a voltage pulse when it should. The absence of an electrical pulse is likely to go undetected.
Furthermore, if a hydraulic cylinder solenoid becomes electrically shorted or open, it will fail to actuate or deactuate a cylinder which can lead to mechanical damage in the machine or to the product which it is producing.
As a further example, solenoid actuated hydraulic cylinders are commonly used on hay balers with the source of operating power for the solenoids being the electrical system of the tractor pulling the hay baler. In such applications, the output voltage from the electrical system can vary from its nominal 12 volts as the electrical load on the electrical system varies. The variable supply voltage supplied to the solenoid makes it difficult to design a test circuit for on-line testing of the electrical integrity of the solenoid--that is, whether the solenoid is electrically open or short. Additionally, an on-line test of an electrical solenoid must be such that the test itself does not actuate the solenoid, a fact which further complicates the design process.
Finally, a system for on-line checking of the integrity of coils, solenoids, or the like is enhanced if the testing is done automatically without the need for operator intervention to initiate the test, and is further enhanced if an alarm is sounded or displayed in the event the coil, solenoid, or the like is defective.